Effects of drought stress on CO 2 exchange and water relations in the CAM epiphyte Tillandsia utriculata (Bromeliaceae)

Abstract

Summary Water was withheld from plants of Tillandsia utriculata L. for up to two months in a growth chamber. Nocturnal CO2 uptake declined substantially in the first week without water, then declined slowly between 7 and 31 d of the drought treatment. Net CO2 exchange after two months of desiccation was nearly zero, although substantial nocturnal increases in malic acid concentrations were still measureable. Thus, the degree of CO2 recycled internally via CAM increased dramatically throughout the drought treatment. In spite of the slow, yet substantial declines in nighttime CO2 uptake observed throughout the drought treatment, leaf water potentials remained relatively high (above −1.5 MPa) and declined by only 0.5 MPa after two months without water. Based on pressure-volume analyses, the leaf bulk elastic modulus was approximately 3.3 MPa, a very low value indicative of highly elastic cell walls. Thus, maintenance of high turgor pressures as a result of elastic cell walls may constitute an important adaptation of this species and presumably other epiphytic species of Tillandsia that reduces the negative effects of drought stress. This, as well as other adaptations to drought stress such as the preferential utilization of water from water-storage parenchyma, osmotic adjustment, and low rates of transpiration, should contribute to survival during drought in these unusual plants.